The present invention relates to a device for measuring changes in pressure, and preferably for checking the tightness of a fuel tank.
For the continuous testing of fuel tanks with respect to their tightness, methods and devices are known in which, after a decrease in pressure which has been produced for test purposes, the change in pressure, i.e. the rate of change of the pressure, is measured in the fuel tank and evaluated. For this, there is generally used a pressure-difference sensor, such as, for instance, in a process and an apparatus for determining the level of fuel in a tank in accordance with Federal Republic of Germany 42 03 099 A1. In that case, the pressure-difference sensor produces a signal which is analogous to the pressure difference between the pressure within the tank and the outside pressure.
A pressure-difference sensor therefore requires venting to the outside, and in this connection there must be assurance that no liquid enters, such as, for instance, water of condensation. The use of labyrinths, capillaries, and Teflon filters does not constitute absolute protection against this. Furthermore, the fuel could escape if the sensitive membrane of the pressure-difference sensor were to burst.